The XSetSelectionOwner function changes the owner and last-change
time for the specified selection and has no effect if the specified time
is earlier than the current last-change time of the specified selection
or is later than the current X server time. Otherwise, the last-change time
is set to the specified time, with CurrentTime replaced by the current
server time. If the owner window is specified as None, then the owner
of the selection becomes None (that is, no owner). Otherwise, the owner
of the selection becomes the client executing the request.

If the new owner
(whether a client or None) is not the same as the current owner of the
selection and the current owner is not None, the current owner is sent
a SelectionClear event. If the client that is the owner of a selection
is later terminated (that is, its connection is closed) or if the owner
window it has specified in the request is later destroyed, the owner of
the selection automatically reverts to None, but the last-change time
is not affected. The selection atom is uninterpreted by the X server. XGetSelectionOwner
returns the owner window, which is reported in SelectionRequest and
SelectionClear events. Selections are global to the X server.

XSetSelectionOwner
can generate BadAtom and BadWindow errors.

The XGetSelectionOwner
function returns the window ID associated with the window that currently
owns the specified selection. If no selection was specified, the function
returns the constant None. If None is returned, there is no owner for
the selection.

XGetSelectionOwner can generate a BadAtom error.

XConvertSelection
requests that the specified selection be converted to the specified target
type:

If the specified selection has an owner, the X server sends a SelectionRequest
event to that owner.

If no owner for the specified selection exists, the
X server generates a SelectionNotify event to the requestor with property
None.

The arguments are passed on unchanged in either of the events. There
are two predefined selection atoms: PRIMARY and SECONDARY.